It has long been desirable to provide automatic control of vehicle lighting both to improve driving safety and provide convenience for the driver. Such automatic lighting control may include automatic activation and deactivation of a controlled vehicle's high beam headlights as a function of driving conditions. This function has been widely attempted using various types of optical sensors to detect the ambient lighting conditions, the head lamps of oncoming vehicles and the tail lamps leading vehicles. Most recently, sensors utilizing an electronic image sensor have been proposed. Such systems are disclosed in commonly assigned U.S. Pat. No. 5,837,994 entitled Control system to automatically dim vehicle head lamps and U.S. Pat. No. 6,049,171 entitled Continuously variable headlamp control and commonly assigned U.S. patent application Ser. No. 09/799,310 entitled Image Processing System to control Vehicle Headlamps or other Vehicle Equipment, Ser. No. 09/528,389 entitled Improved Vehicle Lamp Control, and Ser. No. 09/800,460 entitled System for Controlling Exterior Vehicle Lights. The disclosures of each of these documents are incorporated in their entireties herein by reference. Light source detection within image sensing presents many challenges. For example, it may be difficult to discriminate between oncoming vehicle head lamps and reflections of the controlled vehicle's head lamps off of signs or other objects. Additionally, it may be difficult to detect distant tail lamps in proximity of other light sources, such as overhead street lamps for example, because these light sources may blur together in the image diluting the red color of the tail lamps.
Some of these problems may be solved by higher resolution imaging systems. However, construction of such a system requires a more expensive image sensor, a high quality lens, more processing power and more memory which, at the present time, would be cost prohibitive. Further more, not all of the problems with currently disclosed systems are likely to be solved with increased resolution alone, even disregarding economics.
The present invention seeks to overcome the limitations of the prior art by providing improved methods of acquiring and analyzing images from an image sensor for the purpose of detecting the head lamps of oncoming vehicles and tail lamps of leading vehicles and for discriminating these light sources from other sources of light within an image. The information obtained by the apparatus and methods disclosed herein may be used to automatically control vehicle equipment, such as controlling a controlled vehicle's exterior lights, windshield wipers, defroster, or for other purposes.